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Hubble constant

  1. Nov 14, 2014 #1
    if the speed of the expansion is decreasing then it would mean that the radius of the hubble sphere is increasing because it would require more space to expand faster than the speed of light .but as you said if the speed of expansion is increasing then why is the hubble sphere increasing and
    why is the radius of the hubble sphere derived multiplying the speed of light with the hubble constant where, the the hubble constant is just the percentage of which the space is increasing while all we need to calculate the radius is the speed of expansion and not the percentage .

    if gravity was the answer to my previous questions then does it mean that gravity will eventualy win over and stop the expansion and start bringing things together(leading to the big crush).If so then why is that the universe is expected to turn into a cold dark and empty place?would there be a big crush or the expansion just win over and turn the universe into a vast ,cold,dark,and empty place?

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  2. jcsd
  3. Nov 14, 2014 #2


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    The percentage RATE of distance growth is decreasing. A percentage growth rate is different from a speed.

    The "speed of expansion" is only defined you focus on a particular distance and watch it expand over time.
    If you do that, you will find that its speed of expansion is increasing and (according to standard model) will continue to increase.

    The speed at which a distance increases in size can accelerate even while the percentage growth rate decreases.
    and that in fact is what is actually happening.

    The percentage growth RATE is settling down to 1/173 % per million years. When it has done so we will still have exponential expansion, no "crunch" expected : ^)

    If you have questions about what I or others have said in some specific post, shouldn't you QUOTE the post so we can see what you are confused by?
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